In many localities the sanitary sewer system is overloaded due to the influx of surface water into the sewer system through manholes in the streets. The manhole is normally enclosed with a cast iron cover or lid which rests on an annular shoulder formed in the manhole casting, so that the upper surface of the cover is flush with the road surface. The conventional manhole cover contains from about four to twelve vent holes and surface water flows into the sewer system through the vent holes, as well as through the joint between the cover and the casting which is normally unsealed.
To relieve the burden on the sanitary sewer system, some municipalities have installed new manhole covers without vent holes and have attempted to seal the cover to the casting. However, new covers are costly and require disposal of the old covers, and in many cases, a retrofitted cover does not properly fit within the manhole casting, with the result that there is considerable wobble and rattling of the cover when subjected to vehicle traffic and the wobble causes wear of the cover and casting.